Cardiovascular effects of 2-Br-alpha-ergocriptine in urethane anesthetized rats

Experiments were designed to study the cardiovascular effects of Bromocriptine (2-Br-alpha-ergocriptine) in the normotensive anesthetized rats. The intravenous administration of bromocriptine (20 micrograms/kg and 200 micrograms/kg) produced a long-lasting and not dose-dependent fall in the mean blood pressure and heart rate. The pressor response to phenylephrine, an alpha adrenergic agonist, was antagonized by bromocriptine in a dose-dependent manner. At a dose of 20 micrograms/kg bromocriptine behaved as a competitive antagonist, whereas at the dose of 200 micrograms/kg produced an insurmountable blockade of the response to phenylephrine. Previous administration of phentolamine (5 mg/kg) prevented the insurmountable blockade of alpha adrenoceptors by bromocriptine. This observation suggests that both drugs compete for the same receptor. It is concluded that blockade of peripheral alpha-adrenoceptors may contribute to cardiovascular effects of bromocriptine.